u1 <-
function(x){
	nrm <- two_norm(x[-1])
	n <- length(x)
	if(nrm < 1e-12){
		c(0.5,(-0.5)*rep(sqrt(1/(n-1)),n-1))
	}else{
		c(0.5, (-0.5/nrm)*x[-1])
	}
}

